This invention relates in general to transformer voltage regulators which transmit a significant amount of power from an input voltage source to a load, and more particularly to a transformer regulator which transmits most of the power through some of the transformer windings directly to the load and which regulates only that portion of the voltage which corresponds to the maximum expected deviation of the input voltage control means such that the voltage at the load remains at the desired nominal value despite deviations in the input voltage source.
A.C. voltage sources are ideally designed to supply constant voltage independent of the current load demanded. However, due to a number of factors including physical line resistance, load demanded by other apparatus, control of the A.C. power generating equipment, and various other factors, the A.C. voltage available from a voltage source frequently deviates, either positively or negatively, from the desired nominal value. Not infrequently, this deviation can exceed 10 percent. Many applications exist where such deviation is not acceptable. Often times in such situations, the user must resort to generating his own highly regulated A.C. power rather than using that commercially available from electrical generating utilities.
Many types of transformers are known to the prior art. However, transformers are inherently poor voltage regulators because the output voltage of a transformer is proportionately related to the input voltage applied to the transformer by the turns ratio of the various transformer windings. Thus, any deviation in the input voltage applied to the transformer results in a corresponding proportional deviation in the output voltage of the transformer. That is, conventional transformers proportionately pass any deviation in the input directly to the output. It is therefore typical to concentrate on regulating the output supplied by the transformer by means of a separate voltage regulator interposed between the transformer and the load. While this approach is suitable for low D.C. voltage levels, suitable semiconductors for higher A.C. voltage levels are still quite expensive. Furthermore, the switching characteristics of semiconductors introduces wave form distortion and noise when attempting to reproduce the usual sine wave form typical of A.C. power generation. This necessitates bulky and expensive filtering.
Prior art transformers also suffer from undesirable size and weight disadvantages when 2000 watts or more of power are transmitted. Such transformers also become quite expensive because of the volume of material required to fabricate larger transformers.